Therapies have been developed for treating atrial and ventricular tachycardias by destroying cardiac tissue containing an identified ectopic foci or an aberrant conduction pathway; one of these therapies includes the application of ablative RF energy delivered through a catheter, which may be introduced transvenously into the heart, to a target site via a virtual electrode formed by conductive fluid infused out from a portion of the catheter in proximity to the site. An ablation electrode contained within that portion of the catheter and shielded by a non-conductive porous shell energizes the infused fluid; the rate of infusion and conductivity of the fluid can be controlled to work in conjunction with various electrodes with different surface areas. The creation of the virtual electrode enables the current to flow with reduced resistance or impedance throughout a larger volume of tissue, thus spreading the resistive heating created by the current flow through a larger volume of tissue and thereby creating a larger lesion than could otherwise be created with a ‘dry’ electrode. Furthermore, virtual electrodes reduce the potential for complications arising from an excessive electrode temperature (approximately greater than 100 degrees Celsius), typically associated with ‘dry’ ablation electrodes in direct contact with the target site, which may cause formation of blood coagulum and sub-surface explosions or pops within the tissue.
Physicians have long used the technique of pressing an RF electrode, which terminates a distal end of a catheter, against the endocardium, applying RF energy, and dragging the electrode along the endocardium to create an elongated lesion. Consequently, there remains a need for an improved RF ablation catheter including a virtual electrode assembly that is simple to fabricate and to use efficaciously in this manner.